Roy Keane arrives at his house in Hale, Altrincham last night. Photograph: PA Wire/PA

Roy Keane became so introspective and elusive during the closing period of his time in charge at Sunderland that often the only way Niall Quinn could contact him was by text message. It is understood that was how his resignation as manager was initially delivered to the chairman.

Quinn handled Keane's departure with typical class, generosity and dignity yesterday. "Everybody at the club has got a huge respect for Roy," said Quinn, who stressed that Keane's motives were unselfish and that he had not demanded a pay-off. "He lifted this place off its knees," he added. "Roy Keane hasn't been sacked because we've a bad team, he's resigning because we've a good team he feels he can't bring on any further. There's a big difference there. You hear the term amicable, that's actually the way it is here."

The chairman's polished outward demeanour camouflaged the fraught reality of the preceding few days when an increasingly withdrawn Keane oscillated between a determination to try to revive the fortunes of a side that had lost six of their seven previous games and a desire to quit. Quinn initially offered his manager space over the weekend to think things through and on Sunday travelled to Portugal to "clear" his own head. Keane failed to attend any of Sunderland's training sessions this week - a not uncommon occurrence - and, when Quinn returned to England on Wednesday, the pair failed to determine a viable way forward.

Although Sunderland's board hoped Keane would continue they were concerned that he had lost the support of a dressing room harbouring constantly rotated players who seemed intimidated and alienated by their maverick and temperamental manager. A watershed occurred 10 weeks ago when Sunderland scraped past Northampton Town in the Carling Cup and individuals were shocked at the ferocity with which Keane hurled personal obscenities at them.

Keane could or would not soften his stance, though, and yesterday morning informed Quinn he was not returning. His resignation was subsequently received in a formal fax sent by his solicitor, Michael Kennedy. In an attendant statement Keane said: "I would like to thank my staff, players, Niall Quinn and, in particular, the fans for their support during my time at Sunderland and I would like to wish the club every success in the future." Last night the winger Carlos Edwards said: "The players still had full confidence in him and are kind of let down in a way."

Sam Allardyce quickly made it plain that he would welcome an invitation to manage the club he once played for and later coached at under Peter Reid. "Sunderland are a great club, so of course I'd be interested in talking to them," the former Bolton and Newcastle manager said. "I have huge respect for the chairman, Niall Quinn, and the job he has done.

Meanwhile Phil Brown, a boyhood Sunderland fan, reiterated his commitment to Hull. David O'Leary was among the other early contenders and the former West Ham manager Alan Curbishley was prominent in bookmakers' lists.

The relationship between Keane and Quinn had often been hands-off and conducted by text but gained further distance once Ellis Short, the Irish-American financier, became Sunderland's leading shareholder in September. When Short inquired why Keane had not signed a contract extension to replace the deal due to expire next June and questioned some of the manager's more eccentric and expensive buys, even the diplomatic chairman struggled to maintain harmony.

Six weeks ago things looked deceptively rosy when Sunderland beat Newcastle but already Keane was struggling to control two of his more controversial signings, Pascal Chimbonda and El Hadji Diouf, and the club subsequently slid into relegation trouble. "Roy is his harshest critic and he felt he'd completed his journey here," Quinn said. "We spent three days trying hard to find a solution but he didn't want to come unstuck any further and us find ourselves in deeper, darker territory."

The chairman suggested the stress of Premier League management had taken its toll: "Roy brought amazing standards to this club, his compelling nature changed mind-sets. But the pressure is intense."

Ricky Sbragia, the head coach, will be in charge for tomorrow's trip to Manchester United, aided by the reserve team coach Neil Bailey and the midfielder Dwight Yorke.